In a centrifugal separator, for example, a culture solution, blood, or the like as a sample is poured into a rotor via a tube or a bottle, and the rotor is rotated at high speeds to separate and purify the sample. The rotor has a rotation speed variously set depending on the use purpose, and a group of products from a low speed on the order of several thousand rotations per minute (rpm) to a high speed with a maximum rotation speed of 150,000 rpm have been provided according to use purposes. Rotors for use have various types, such as an angle rotor with a tube hole being of a fixed angle type that can support a high rotation speed and a swing rotor with a tube-inserted bucket swinging from a vertical state to a horizontal state according to the rotation of the rotor. Also, rotors have various sizes, such as a rotor applying a high centrifugal acceleration to a small amount of sample by rotation at an ultra-high rotation speed and a rotor that can handle a large amount of sample although the rotation speed is low. Any of these rotors is selected according to the sample to be separated. Therefore, the rotor is configured so as to be attachable to and removable from the rotating shaft of a driving unit such as a motor, and can be replaced.
When the rotor rotates at a high speed in the air, the temperature of the rotor increases by frictional heat with air (windage loss). Depending on the sample to be separated, the temperature has to be kept low. Therefore, a centrifugal separator in which the rotor is cooled during operation has been widely used. A cooling centrifugal separator has a main body provided with a cooling device (such as a freezing device configured of an evaporator, a compressor, a condenser, and an expansion valve). The inside of a rotor chamber is cooled by letting a refrigerant flow through a copper pipe wounded around the outer perimeter of a bowl at an outer wall of the rotor chamber, thereby indirectly cooling the rotor. In a cooling centrifuge, as also described in Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 2012-11358), temperature conditions capable of controlling the temperature of the rotor are described in an instruction manual. In general, the rotor can be used but temperature control by the rotor may not be possible within the specifications. The use environment temperature is room temperatures from 2° C. to 40° C. Of these, performance-assured temperatures with which it is assured that temperature control by the rotor can be within the specifications are room temperatures from 15° C. to 25° C.
Here, the structure of a conventional centrifugal separator is described by using FIG. 12. The centrifugal separator is provided with a bowl 2 formed of a metal thin plate inside a casing 6 made of a box-shaped sheet metal. The bowl 2 and a door 5 define a rotor chamber 3, and the rotor chamber 3 is sealed with a door packing 12. A rotor 1 holds a sample to be separated and rotates the sample at high speed. The rotor 1 has a plurality of holes (not shown) formed for insertion of a tube or the like for pouring the sample, and is supported by a rotating shaft of a motor 4 as a driving part. The rotor 1 is rotated by the motor 4, and the rotation of the motor 4 is controlled by a control device 114. The door can rotate in a vertical direction with a hinge 11 being taken as a center axis. At the rear of the door 5, an operation panel 13 is placed for a user to input conditions such as a rotation speed of the rotor and a separation time and to display various information items. The operation panel 13 can function as both a display unit and an input unit when a so-called touch-panel liquid crystal display device is used.
The rotor chamber 3 is configured so that an opening on an upper side can be sealed by the door 5. With the door 5 open, the rotor 1 can be attached to or removed from the inside of the rotor chamber 3. The bowl 2 has an outer perimeter around which a copper pipe 7c as an evaporator is wounded in a spiral shape. The copper pipe 7c has an outer perimeter surrounded by a cylindrical insulating material 17. At a lower part of a main body of the centrifugal separator, a freezing device 107 configured to include a condenser 7a and a compressor 107b is placed, and the copper pipe 7c is connected to the compressor 107b. Also, an air-blowing device 10 is installed at a back surface of the main body for heat dissipation of the freezing device 107, taking a wind in from an intake port 8 opening at a bottom part of the front surface of the main body and exhausting air from an exhaust port 9. Arrows in FIG. 12 show an air flow from the intake port 8 to the exhaust port 9 through the condenser 7a. A refrigerant is sent from the compressor 107b into the condenser 7a, and the cooled refrigerant is liquefied by the condenser 7a and the air-blowing device 10. The liquefied refrigerant is supplied through a capillary 7d to the copper pipe 7c, and the inside of the rotor chamber 3 is kept constant at a desired temperature set under control by the control device 114 during operation of centrifugation. The temperature of the rotor 1 is monitored by the control device 114 by using an output from a temperature sensor (not shown) installed in the rotor chamber 3.
As the freezing device 107 for use in a centrifugal separator, a reciprocal compressor or a rotary compressor has been generally adopted so far as described in Patent Document 2 (Japanese Patent Application Laid-Open Publication No. 5-228400) and Patent Document 3 (Japanese Patent Application Laid-Open Publication No. 5-228401), and temperature control is performed by ON-OFF control of intermittent driving between operation and stopping, that is, a duty-ratio control. Meanwhile, even in centrifugal separators, not only energy saving and space saving but also high efficiency and ecology are keywords in recent years when customers purchase products.